Electromagnetic indicator



Nov. 14, 1961 B. M. GORDON ELECTROMAGNETIC INDICATOR 2 Sheets-Sheet 1 Filed April 25, 19-57 T a- I m m6 M D R A N R E B A TTOR/VE Y Nov. 14, 1961 B. M. GORDON ELECTROMAGNETIC INDICATOR 2 Sheets-Sheet 2 Filed April 25, 1957 wvavroR BERNARD M. GORDON 5r f ATTORNEY 3,089,140 ELECTROMAGNETIC INDICATOR Bernard M.Gordon, Newton, Mass, assignor to Epsco,

Incorporated, Boston, Mass, a corporation of Massaclausetts Filed Apr. 23, 1957, Ser. No. 654,533 Claims. ((Il. 340-319) The present invention relates in general to data display apparatus, and more particularly, to novel and improved means for reliably activating an electromagnetic character indicating device of the type described in the copending application of Bernard M. Gordon, Hector Durocher, and Americo Sico, entitled Electromagnetic Indicator, Serial No. 641,932, filed February 25, 1957, now Patent No. 2,943,313.

The aforesaid copending application disclosed an electromagnetic data display device of simplified design and construction, with positive, unambiguous, high speed character selection and presentation wholly without complex pawl and ratchet linkages, electronic circuits and components, particularly adaptable to low cost mass production techniques. The invention employed a character bearing member in association with an electromagnetic structure selectively energizable to produce any one of a plurality of discrete magnetic field orientations. A magnetic device Whose motion was controlled by the selected field determined the displacement of the character member, and a viewing window was provided for visual observation of the chosen character. For each inscribed figure displayed, two closely adjacent, magnetically determined stable positions were available for the character bearing member, one fixed by the electromagnetic structure when electrical excitation was applied thereto, and the other by an independent static magnetizable member which coacted with the magnetic device associated with the character bearing member in the absence of electrical excitation. This permitted precise, unambiguous centering of each of the characters to be displayed, provided a restraining torque which precluded drift of the character bearing member due to environmental disturbances, such as vibration, and of special significance, furnished a magnetic circuit without dead spots or conditions of magnetic equilibrium which would otherwise tend to prevent the development of displacement forces upon the character member despite the applied excitation.

The switching means illustrated in the aforesaid application for orienting the stator magnetic field to effect display of the desired character was of the multiple-throw double-pole variety. That is to say, whenever it was desired to change the orientation of the stator magnetic field, two diametrically opposed connections had to be changed.

The present invention contemplates and has as a primary object the provision of a circuit permitting the use of a single pole multi-position switch for selecting the desired indica. That is, when it is desired to change the orientation of the stator magnetic field, only a single connection need be changed. Thus, all the advantages and features enumerated above and associated with the novel electromagnetic data display device are retained, while the complexity of the selective energizing and switching means is appreciably reduced. By using but a single movable contact, mechanical alignment problems are avoided. Should it be desired to utilize electronic switching, application of the inventive concepts results in a marked reduction in the number of components required in the associated circuits. Whether mechanical or electrical switching means are used, the simplified switching structure results in an increase in operational reliability.

In one aspect of the invention, a circular stator core supports a symmetrical, circular configuration of electromagnets capable of establishing a discrete number of magnetic field orientations in response to the selective application of current to the coils thereof. Impedances couple each junction between adjacent coils to a common terminal of a potential source. In addition, each of these junctions is connected to a tap on a multi-position switch, the movable arm of which is returned to the other terminal of the potential source. In a representative form of the invention, there are an even number of coils having like characteristics and the impedances, in the form of fixed resistors, joining each junction to the first potential source are of the same value.

Other features, objects and advantages of the invention will become apparent from the following specification when read in connection with the accompanying drawing in which:

FIG. 1 is a perspective view of one of the data indicating units controlled by the novel switching means embodying the principles of this invention;

FIG. 2 is a schematic circuit diagram illustrating the electrical interconnection of the electromagnets within the indicating device of FIG. 1 and a multiple-throw, double-pole switching means for actuation thereof;

FIG. 3 is a side view, bro-ken in part, and serves to illustrate the relative angular orientation of components of the indicator under a particular electrical condition; and

FIG. 4 is a schematic circuit diagram illustrating the electrical interconnection of the electromagnets within the indicating device of FIG. 1 and the improvements in the switching means for actuation thereof.

Throughout the several views of the drawing, like reference numerals will be used to designate like components.

With reference now tothe drawing and more particularly to FIG. 1 thereof, there is shown a perspective view which generally illustrates the external physical characteristics of the indicator under discussion. For a full description of the structural and operational details, reference is made to the copending application; however, for present purposes certain significant portions of that application will be repeated here,

All electrical and mechanical elements of the device are completely enclosed within a thin cylindrical housing 11, formed with a single rectangular window 12, through which the digits inscribed upon the outer cylindrical surface of a coaxial rotor 13, may be viewed.

A multiplicity of wires 14 (whose internal connections are described below) extend from the indicator for connection to an external circuit for electrical control of the digit presentation. The circular end wall of rotor 13 is seen to contain a plurality of relatively large perforations 15 which advantageously function to minimize the inertia of the rotor and as a consequence enhance the speed of response to external signals. Rotor 13 comprises a central hub 16 which diverges into an integral substantially circular side wall 17 which in turn supports the thin, integral character bearing cylindrical surface 18. For convenience the description which follows will refer primarily to a device capable of displaying a selected one of ten different digits. It is to be understood that selection from a difiierent number of symbols is within the scope of the invention.

With reference now to FIG. 2, the technique of selecting the character to be displayed by a multiple-throw double-pole switch, as disclosed in the previous application, will be discussed briefly.

Each of the wires 14, which may be color-coded for convenience in installation, is shown brought to terminals such as 21 and 2,2. A D.C. source, illustrated as battery 23, energizes the coils through rotatable switch arms 24 Patented Nov. 14, 1961 and 25, mechanically ganged, as diagrammatically indicated by broken line 27, the switch arms being spaced to contact diametrically opposite terminals such as 21 and 22. The effect of the circuit shown is to set up a current I which divides equally between opposite symmetrical semi-circles of the coils 26. The net effect of both currents 1/2 is to establish a diametrical magnetic field designated by the vector B.

The field represented by vector B is one of the ten possible discrete diametrical magnetic fields which may be created by rotation of switch arms 24 and 25. Each of these fields, which has the efiect of displaying a respective digit, will be separated from adjacent fields by the angular separation of adjacent coils 26. For the decimal indicator, this is 36; however, some variation in this distribution may be expected because, as discussed in the aforesaid copending application, a high degree of precision was not a primary requirement in mounting coils 26 on the supporting core.

Although rotation of opposed switch arms 24 and 25 is effective in rotating vector B, it should be apparent that this is not the only means by which a desired field orientation may be established. For example, if an indicator unit is used as a computer output device, all ten wires 14 may be directly coupled to the computer, and energization of any two opposite wires will set up a field and select a digit for display. The selective energization means may utilize mechanical or electronic switching.

The schematic diagram of FIG. 2 illustrates the wiring symmetry of the circular array of coils 26 about the magnetic core (not shown in this figure). Conventional dot notation has been used to indicate winding direction, and it is seen that the dotted end of each coil is joined to the undotted end of the next adjacent coil. Insofar as the magnetic field is concerned, this is effectively the equivalent of winding 21 tapped, continuous toroidal winding upon core 28.

Reference is now made to FIG. 3 for illustration of the relative orientation of certain of the key components in the assembled indicator, and for a discussion of the significance and utility of the magnetic elements discussed above. This cutaway drawing illustrates coils 26 symmetrically arranged on core 28 which effectively forms a closed loop of material having a low magnetic reluctance. The core is preferably formed of a plurality of stacked iron laminations. Each of the laminations comprises a flat circular stamping of magnetic material which is formed with a relatively narrow slit 31. In assembling the magnetic structure the requisite number of laminations are placed one upon the other with the slits 31 in transverse alignment. At this point, the laminations as a group are bent open, forming a helical core, and for the decimal indicator under discussion, ten coil forms 32, each wound with a respective solenoid-type coil 26, are slipped onto the magnetic structure. The coil forms 32 are so dimensioned as to abut one another along the inner circular edge thereof when in position. This arrangement makes it unnecessary to use spacers or other means to assure a reasonably symmetrical distribution of coils 26 about core 28.

With the coils in place, the laminar core structure is allowed to spring back to its normal circular form, and to avoid an abrupt air gap, a screwdriver or like implement is used to rotate each of the laminations with reference to the others so that the respective slits 31 are symmetrically distributed. For example, when using five laminations, each of the circular elements may be shifted so that the angular spacing between adjacent slits is approximately 72 degrees. Under the circumstances, the effect of the individual air gaps 31 is negligible. The number of currents in each of the solenoidal coils 26 will be determined by design factors, such as applied voltage, but for general application may consist of several thousand turns of relatively fine wire.

Wires 14 which are used for external actuation extend from the respective junctions between each two adjacent coils (see FIG. 2). The wires interconnecting the adjacent coils 26 are not shown in FIG. 3 but the group of output wires 14 have been illustrated in FIG. 3. Evidently, the number of output wires 14 is exactly equal to the number of coils used upon the toroidal magnetic core 28, and for a decimal display device this number, of course, is ten.

The salient pole permanent magnet 33 is secured to rotor 16 (not shown in FIG. 3) whereby the latter follows the motion of the former. The peripheral air gap between permanent magnet 33 and the ring of solenoid coils 26 accommodates a relatively thin non-magnetic cylinder 34. This element is formed with small rectangular slots equal in number to the stator coils 26, and accordingly equal in number to the characters to be displayed. These slots are separated by precisely equal angles measured about the axis of the cylinder; thus, for the decimal unit illustrated, the exact angular separation between adjacent slots is thirty-six degrees. Each slot accommodates a static magnetizable element 35, preferably in the form of rectangular iron bars firmly cemented or otherwise afiixed within the respective slots. Each magnetizable element 35 is angularly displaced from the earest point of abutment of adjacent coil forms 32 by an angle 0.

Line 36 has been drawn for reference purposes from the center through a point midway between two adjacent coil forms 32. The purpose of this line is to define the position of one of the ten discrete magnetic field vectors B, such as the one shown upon the circuit diagram FIG. 2.

Thus, these figures show that cylinder 34 is fixed Within the stator and oriented within housing 11 so as to provide a substantially uniform angular separation, designated on the drawing as 0, between the individual magnetic elements 35 and the respective midpoints between adjacent electromagnets. With current flowing as in FIG. 2, and assuming that the device is in perfect adjustment, salient pole magnet 33 will rapidly rotate and align itself so that its internal magnetic field is aligned with the field vector B, FIG. 3; the sharply defined N and S (not shown) poles falling along line 36. If now the current I is cut off, the magnetic field designated by vector B disappears, with the result that the force of attraction between each of the salient poles of magnet 33 and the immediately adjacent magnetic element 35 will cause angular rotation of the magnet, and the attached rotor, to a rest position whereby the pointed tip of magnet 33 is aligned along line 37 and directly opposite the immediately adjacent magnetic element 35.

Thus, speaking generally, for each of the ten discrete orientations of the magnetic field vector B in the decimal device being considered, there exists a fixed, stable angular position for magnet 33. In addition, in the region of each of these ten discrete orientations, there exists a second stable position for magnet 33. In addition, in the region of each of these ten discrete orientations, there exists a second stable position for magnet 33 which is defined by the respective magnetic element 35. Stated otherwise, when power is applied to a particular opposite set of input terminals, rotor 13 is brought to a first stable position where it remains until power is cut off; immedi' ately thereafter, the rotor is pulled through the slight angle 0 by magnetic forces to the second stable position. Change in rotor orientation is effected by selective orientation of the stator field which in turn is accomplished by energizing the coils through the two ganged rotating switch arms 24 and 25. The specific advantages of the magnetic configuration are fully discussed in the aforesaid copending application.

With reference now to FIG. 4, there is illustrated a schematic circuit diagram of the novel switching means whereby a multiple-throw single-pole switch may be utilized to selectively orient the stator magnetic field. Each of the coils 26 is represented as an inductance serially-connected to a distributed resistance, designated as L and r, respectively, with a corresponding subscript designating its position in the ring. Conventional dot notation has been used to indicate winding direction and it is seen that the dotted end of each coil is coupled to the undotted end of the next adjacent coil. One terminal of a potential source, represented as battery 23, is connected to each junction between adjacent coils in the ring by respective resistors R to R A source of ground or reference potential at terminal 41 is connected to the opposite end of battery 23, and a selected one of the junctions between adjacent coils by rotating switch arm 42, in this case the selected junction being junction 43 to effect a field orientation at the center of the stator represented by the vector B. Inductances and distributed resistances on the clockwise side of the selected junction 43 have been designated by subscripts l to 5, while the inductances and distributed resistances associated with coils on the counterclockwise side of junction '43 bears the same numerical subscript as its mirror image on the clockwise side, but with a prime thereafter. In the decimal indicating device of this example, there are ten coils, five to the clockwise side of junction 43, and five to the counterclockwise side thereof.

Having thus described the physical arrangement of the novel switching means and the associated coils, the mode of operation will be described. With the exception of the current flowing through resistor R which resistor is directly connected to the selected junction 43, the current flowing from battery 23 through each resistor to terminal 41, maintained at ground potential, has two paths, one clockwise and the other counterclockwise. Each of these current components through the resistors is represented by an arrow indicating the direction of current flow and labeled I bearing a numeral subscript the same as that of the associated resistor and a letter subscript CCW or CW, respectively indicative of counterclockwise and clockwise current flow about the ring. The resultant current flowing through a particular coil in the ring is the algebraic sum of the clockwise and counterclockwise currents flowing therethrough and is represented by an arrow labeled i and bearing a subscript identical with that of the associated inductance. The orientation of the arrow indicates the direction of current flow through the associated coil.

In the preferred embodiment, each coil has substantially the same parameter values, the distributed resistance of each being a value r. Each fixed resistor is of value R. Under these conditions, the magnitude of the two coil currents 1' bearing the same numerical subscript are substantially the same, but flow in opposite directions about the ring. Hence, the magnetomotive force produced by a coil in the ring is substantially equal to that produced by a coil angularly spaced by the same amount from the selected junction 43, but of opposite sense. In general, where there are an even number N of individual coils, the magnitude of both currents i and i is given by the summation:

It is seen that there are no clockwise current components in the current i while there are no counterclockwise current components in the current component i The current through any of the remaining coils is a result of the algebraic summation of the clockwise and counterclockwise currents passing therethrough. Moving away from the selected junction 43, the magnitude of current of same and opposite direction to the resultant current i is seen to respectively decrease and increase; hence, the resultant current i decreases in magnitude. Accordingly, i and i are the coil currents of smallest magnitude. However, the magnetomotive forces produced by each semicircular half of the ring bounded by the diameter passing through switch arm 42 are exactly equal,

but of opposite sense since such force is thesum of the individual magnetomotive forces provided by each coil of the semicircle. Consequently, the orientation of the magnetic field in the center of the stator is as indicated by the vector B.

While in this example components are utilized having like parameter values in a symmetrical arrangement, the principles of the invention apply to a non-symmetrical configuration wherein the parameters are not necessarily of the same value. In such applications the selected orientations of the magnetic field may not be separated by an even number of the same angular increment.

All advantages of the novel electromagnetic symbol indicating device disclosed in the aforesaid copending application have been retained while elfecting a marked reduction in the complexity of the means for selecting display of the desired symbol and increasing the reliability with which such selections may be made.

It is apparent that those skilled in the art may make numerous modifications of and departures from the specific embodiment described herein. Consequently, the invention is to be construed as limited only by the spirit and scope of the appended claims.

What is claimed is:

1. Electromagnetic indicating apparatus comprising an indicator structure formed with a closed ring of serially connected magnet coils defining a generally circular region, a character bearing member having a magnet rotatable Within said circular region, a common terminal, impedance elements respectively permanently coupling each junction between adjacent ones of said magnet coils to said common terminal, and means for selectively coupling a character selection signal between said common terminal and one of said junctions between adjacent coils, said character selection signal being thereby effective to establish a discrete diametrical magnetic field within said circular region for angularly orienting said magnet and character bearing member.

2. Electromagnetic indicating apparatus as in claim 1 wherein said impedance elements are resistors of equal value.

3. Electromagnetic indicating apparatus comprising an indicator structure having a closed ring of serially connected magnet coils disposed upon an endless loop of low reluctance magnetic material, a character bearing rotor structure including a salient pole permanent magnet rotatable within said closed loop, a common terminal, impedance elements respectively permanently coupling each junction between adjacent ones of said magnet coils to said common terminal, a source of control signals, means for impressing said control signals between said common terminal and a selected one of said junctions thereby establishing opposed magnetomotive forces on opposite sides of said closed loop and a diametrical magnetic field within said circular region, said permanent magnet being responsive to said magnetic field and angularly positioning said character bearing rotor structure in a discrete orientation determined by the selected junction.

4. Electromagnetic indicating apparatus as in claim 3 wherein said impedance elements are resistors of equal value.

5. Electromagnetic indicating apparatus as in claim 3 wherein said serially connected magnet coils are of even number, each with a like number of turns.

6. Electromagnetic indicating apparatus comprising an indicator structure having a closed ring of serially connected magnet coils disposed upon an endless loop of low reluctance magnetic material, a character bearing rotor structure including a salient pole permanent magnet rotatable within said closed loop, a common terminal, a terminal individual to each of the junctions between adjacent ones of said magnet coils, resistors of substantially equal value respectively permanently connecting each of said individual terminals to said common terminal, a source of control signals, and switching means for selectively applying said control signals between said common terminal and one of said individual terminals for establishing a diametrical magnetic field in said circular region for activating said rotor permanent magnet.

7. Electromagnetic indicating apparatus comprising an indicator structure having a closed ring of serially connected magnet coils disposed upon an endless loop of low reluctance magnetic material, a character bearing rotor structure including a salient pole permanent magnet rotatable within said closed loop, a common terminal, a ter minal individual to each of the junctions between adjacent ones of said magnet coils, resistors of substantially equal value respectively permanently connecting each of said individual terminals to said common terminal, a source of control signals, and a single pole multiple-throw swtich for selectively applying said control signals between said common terminal and each of said individual terminals for establishing a diametrical magnetic field in said circular region for activating said rotor permanent magnet.

8. A character indicating device comprising, a generally cylindrical housing, a circular array of serially connected electromagnets forming a stator disposed within and aifixed to said housing, a rotor including a salient pole magnet rotatable within said array of electromagnets and a character bearing member having a cylindrical surface rotatable in the region between said electromagnets and said housing, a circular array of magnetic elements disposed in the region between said salient pole magnet and said electromagnets, a window in said cylindrical housing for displaying a portion of said character bearing member, a source of control signals having first and second terminals, resistors of like value permanently connected between the junctions of adjacent electromagnets and said first terminal, and means for selectively connecting said second terminal to one of said junctions whereby said salient pole magnet is aligned along the diametrical magnetic field produced by and within said circular array of electromagnets to display in said Window a portion of said character bearing member as a function of the junction connected to said second terminal.

9. Electromagnetic indicating apparatus comprising, an indicator structure formed with a closed ring of serially interconnected magnet coils defining a generally circular region, a magnet rotatable within said circular region, a first terminal, impedance elements respectively permanently coupling each junction between adjacent ones of said magnet coils to said first terminal, a second terminal, a source of power connected between said first and second terminals, and selective switching means for connecting said second terminal to a selected one of said junctions between adjacent coils to establish a discrete diametrical magnetic field within said region orienting said rotat able magnet.

10. Electromagnetic indicating apparatus in accordance with claim 9 wherein said impedance elements are resistances having substantially the same value.

References Cited in the file of this patent UNITED STATES PATENTS 594,979 Barrett Dec. 7, 1897 1,058,545 Caldwell Apr. 8, 1913 1,366,832 Pierce Jan. 25, 1921 2,649,559 Wargo Aug. 18, 1953 2,665,343 Benson Ian. 5, 1954 FOREIGN PATENTS 137,150 Great Britain Jan. 8, 1920 

